Large surface conductance and superconductivity in topological insulator microstructures

Controllable geometric manipulation via micromachining techniques provides a promising tool for enhancing useful topological electrical responses relevant to future applications such as quantum information science [P. J. W. Moll, "Focused ion beam microstructuring of quantum matter," Annu. Rev. Condens. Matter Phys. 9, 147 (2018); Jang et al., "Observation of half-height magnetization steps in Sr2RuO4," Science 331, 186 (2011); Moll et al., "Transport evidence for Fermi-arc-mediated chirality transfer in the Dirac semimetal Cd3As2," Nature 535, 266 (2016); Moll et al., "Evidence for hydrodynamic electron flow in PdCoO2," Science 351, 1061 (2016)]. Here, we present microdevices fabricated with a focused ion beam from an indium-doped topological insulator Pb1-xSnxTe. With the device thickness on the order of 1 mu m and an extremely large bulk resistivity, we achieve an unprecedented enhancement of the surface contribution to about 30% of the total conductance near room temperature. The surface contribution increases as the temperature is reduced, becoming dominant below approximately 180 K, compared to 30 K in millimeter-thickness crystals. In addition to the enhanced surface contribution to normal-state transport, we observe the emergence of surface superconductivity below 6 K. Measurements of magnetoresistivity at high magnetic fields reveal a weak antilocalization behavior in the normal-state magnetoconductance at low temperatures and a variation in the power-law dependence of resistivity on temperature with the field. These results demonstrate that interesting electronic responses relevant to practical applications can be achieved by suitable engineering of single crystals. Published under license by AIP Publishing.